One way in which power is supplied to a portable computer is by using a power adapter. The power adapter is coupled to an alternating current (AC) power source (such as an AC outlet) and converts an AC line voltage to a lower, direct current (DC) voltage suitable for use by the portable computer. The power adapter is typically a unit that is separate from the portable computer. A portable computer is designed to be moved. When a portable computer is moved to a new location, a power adapter is often brought to the new location along with the portable computer. As result, it is desirable to reduce the size and weight of the power adapter in order to facilitate the movement of the power adapter.
Typically, a portable-computer power adapter is designed to output a particular nominal output voltage for load currents up to a particular maximum current level. When the load current reaches or exceeds the maximum current level, the power adapter reduces the output voltage in order to attempt to prevent the load current from exceeding the maximum current level. Reducing the output voltage in this manner is referred to as “current limiting” the power adapter.
Typically, the power adapter powers various components of the portable computer (including, for example, a central processing unit (CPU), display, and a storage device such as an internal hard drive). In some situations, the power adapter also provides power to charge a battery housed within the portable computer. Moreover, in some situations, the power adapter provides power to one or more peripherals or other devices coupled to the portable computer (for example, a docking station or an external drive unit such as a CD, DVD, or floppy drive unit). Consequently, a portable-computer power adapter is typically used to provide power to a variety of loads.
One way in which a portable-computer power adapter is designed to work with a variety of loads is to design the power adapter for the largest load that the power adapter is expected to power. Designing a power supply in this way, however, typically results in a power adapter that is larger, heavier, and/or more expensive than a power adapter designed to provide less power.
One way in which the size, weight, and/or cost of the power adapter can be reduced is by reducing the largest load that the power adapter is expected to power. As a result, a power adapter that outputs less power can be used to power the reduced largest-expected load. One way in which the largest-possible load can be reduced is by reducing the amount of power consumed by the portable computer (for example, by reducing the clock frequency at which the portable computer's CPU is operated and/or by reducing the amount of power used to charge a battery housed within the portable computer). This reduction typically results in a degradation in the portable computer's performance (for example, by reducing the speed at which a CPU executes program instructions and/or increasing the amount of time required to charge a battery).
Like reference numbers and designations in the various drawings indicate like elements.